The present application claims priority to Japanese Application No. P11-132104 filed May 13, 1999 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a mounting structure of a semiconductor device, and a process for mounting a semiconductor device on a mounting substrate such as a printed circuit board having conductor patterns on which the semiconductor device with a plurality of bump electrodes is mounted.
2. Description of the Related Art
Conventionally, a flip chip bonding process is widely employed, where a semiconductor device is mounted on a printed circuit board (as a mounting substrate) by a facedown bonding method. In this mounting process, as shown in FIG. 9, a plurality of bump electrodes 14 having end surfaces 14A as shown in the figure are bonded on aluminum electrode pads 12 provided on a semiconductor device 10.
After the bump electrode 14 is bonded on the aluminum electrode pad 12, each tip of the bump electrode 14 of the semiconductor device is subject to a leveling process by a leveler made of a material such as brass, so that all end surfaces 14A have the same height and have relatively large area as shown in FIG. 9. The leveling process is done with a load weight approximately expressed by Nxc3x9750 gram-force, where the N is the number of bonding pads formed on the semiconductor device 10.
Then as shown in FIG. 10, when the semiconductor device 10 is mounted on a printed circuit board 20, the bump electrode 14 of the semiconductor device 10 is positioned to conductor patterns 22 formed on the printed circuit board 20. Then heat and pressure are added to the bump electrode 14 from backside of the semiconductor device 10, thereby the bump electrode 14 is bonded on the conductor pattern 22 of the printed circuit board 20.
A filler 30 of thermosetting resin is filled between the semiconductor device 10 and the printed circuit board 20 to seal gaps there-between.
In this conventional method of mounting a semiconductor device on a printed circuit board as above described, there is a defect that foreign body such as a resin particle or something like that is easily put between the end surface 14A (top surface) and the conductor pattern 22 of the printed circuit board 20 during the mounting process. Resultantly, the reliability of a semiconductor mounting process is degraded. For example, the foreign body undesirably put therebetween deteriorates contact condition of the end surface 14a with the conductor pattern 22, and this degrades reliability and productivity of a final product that is installed thus processed printed circuit board.
An object of the invention is to provide a mounting structure of a semiconductor device, and a process for mounting a semiconductor device on a mounting substrate such as a printed circuit board having conductor patterns on which the semiconductor device with a plurality of bump electrodes is mounted.
Another object of the present invention is to provide a new mounting structure of a semiconductor device, and a process for mounting a semiconductor device on a printed circuit board, wherein it is avoided for foreign bodies such as resin particles to be put between a bump electrode of the semiconductor device and a conductor pattern of the printed circuit board.
Further another object of the present invention is to provide a new mounting structure of a semiconductor device, and a process for mounting a semiconductor device on a mounting substrate, wherein there is formed a bump electrode having an acute tip such as cone-shaped top on the semiconductor device to be mounted on the printed circuit board by a facedown bonding method.
In order to over the above-described defects which existed in the conventional mounting structure, it is proposed a new mounting structure, wherein there is provided an acute tip at each bump electrode of a semiconductor device when mounting the semiconductor device having a plurality of bump electrodes on a mounting substrate having conductor patterns.
These acute tips of the bump electrodes are slightly made flat by a leveler with a relatively light load weight, then depressed slowly on the conductor patterns of the mounting substrate with heat and pressure. Resultantly, each bump electrode and conductor pattern are joined with face contact by gradually transforming the shape of the bump electrode including the acute tip thereof.
In the process of mounting a semiconductor device having a plurality of bump electrodes on the conductor pattern of the mounting substrate according to the present invention, the process comprises the steps of a bonding step for providing a plurality of bump electrodes having acute tip on electrode pads of the semiconductor device, a leveling step for slightly making flat the acute tip of the bump electrodes by a leveler with relatively light load weight, a positioning step for positioning the tip of the bump electrode on the conductor pattern of the mounting substrate, and a mounting step for depressing the tip of the bump electrode against the conductor pattern slowly with heat and load weight. During this mounting step, the bump electrode and the conductor pattern of the mounting substrate are bonded with face contact while transforming shape of the bump electrode gradually.
In the mounting structure for the semiconductor device according to the present invention, each bump electrode of the semiconductor device has an acute tip formed on top of the bump electrode before mounting. Each acute tip of the bump electrode is preferably flattened slightly with relatively light load weight. And the tip of the bump electrode is positioned on the conductor pattern of the printed circuit board and pressed slowly against the conductor pattern with pressure and heat. Each tip of the bump electrode is gradually transformed and joined to the conductor electrode with face contact.
According to the present invention, each tip of the bump electrode has only small top surface before mounting, so that during mounting process it is avoidable to put foreign body between the bump electrode and the conductor pattern of the printed circuit board.
Namely the tip of bump electrode is gradually transformed by being pressed against the conductor pattern of the mounting substrate, and this transformation of the bump electrode pushes out foreign body existed between the bump electrode and conductor pattern from inside to outside, and finally the bump electrode is transformed as to perform a face contact with the conductor pattern while excluding foreign body.
Therefore, foreign bodies are seldom put between the conductor pattern and the bump electrode.
According to the present invention, it is easily performed to obtain a good contact condition between the bump electrode and the conductor pattern, and thereby a reliability and productivity of a final product are improved.
In the method for mounting the semiconductor device on the mounting substrate according to the present invention, at first a plurality of bump electrodes having acute tip is provided on each of an electrode pad formed on a semiconductor device at a bonding process. In the following leveling step, each tip of the bump electrode is flattened slightly by a leveler with a light load weight. Then each tip of the bump electrode of the semiconductor device is positioned on a conductor pattern of a mounting substrate in a positioning step. Then the semiconductor device is depressed against the mounting substrate with load weight and heat in a next mounting step. In this mounting step, each top of the bump electrode is slowly depressed on the conductor pattern of the mounting substrate, and is gradually transformed so as to perform face contact condition between the transformed bump electrode and the conductor pattern.
In order to make an acute tip at each top of the bump electrode, a conglobation is formed at an end of a gold wire having a diameter of about 25 xcexcm by an electric discharging at first. Then thus formed conglobation of the gold wire is depressed on the aluminum electrode pad 112 with an ultrasonic heating for making alloy of gold and aluminum, and after that the gold wire is pulled off as to form the acute tip on the bump electrode.